It is easy to have misleading intuitions about the population genetic effects of a short, sudden bottleneck. For example, Ernst Mayr suggested that many species had passed through extreme bottlenecks in founder events. He argued that extreme loss of diversity in such events would promote evolutionary change.

The matter was taken up at The Skeptical Zone where population geneticist Joe Felsenstein, among others, replied, skeptical but not ruling the idea out.

Now Buggs has replied at the Zone to comments by Felsenstein and Schaffner:

First, I note that both Schaffner and Felsenstein agree with my point that the bottleneck hypothesis has not been directly tested.

Schaffner: “Buggs is right that existing tests have not been tested rigorously against an ancient Adam and Eve scenario. On the other hand, no one has shown that such a scenario would be undetectable by those tests either; it’s just not a scenario most geneticists are interested in.”

Felsenstein: “Most of the effort in analyzing these data has been to infer the past history of population size, rather than to make statements about A&E.”

Felsenstein goes further than this and suggests that it could never be entirely disproven: “If one poses the problem as whether we can absolutely certainly rule out A&E, that is asking for more than science can deliver. But if we ask whether it is made very improbable, that is not as hard to establish.”

Second, I note that neither of them are defending the PSMC argument, and Felsenstein implies that it is not necessarily reliable and new methods need to be developedMore.

In short, we don’t know that a single human pair Adam and Eve, could not have been the human founders unless we adopt a theory to which evidence is irrelevant. Cosmology’s multiverse springs immediately to mind but does evolutionary genetics want to go There?

Note: At odd moments in these times, biology sounds more sensible than physics.

See also: Adam and Eve debut at the Skeptical Zone: In other words, we don’t really know if they could have existed because the human race seems very improbable anyway. But it is high time the question was liberated from the Sunday armchair of theistic evolution, to say nothing of its occasional personal dramas.

Strictly disallowing a first pair of humans, how did we get from ZERO homo sapiens to 10,000 homo sapiens?

The arguers against 2 humans producing all subsequent humans (over the course of many generations) seem to be arguing that lots and lots of monkeys managed to produce lots and lots of fully human offspring until there were 10,000 or more bona fide homo sapiens. But when we hit 10,000, SUDDENLY humans began mating with other humans instead of the legendary Missing Links.

Does this work the same way for new species of ANY other plant or animal? I mean, did now extinct European Flying Squirrels produce 10,000 bats who then SUDDENLY started mating with other bats instead of the assumedly more available Flying Squirrels?

Also, if you look at primitive humans alive today, I don’t believe 10,000 Bushmen EVER come together. And the same is true for chimps and gorillas and orangs: large primates simply DON’T live in herds like zebras. Or at least didn’t until the rise of cities only a few thousand years ago.

But I wanna hear more about getting from ONE to 10,000 without going through TWO.

Surely on the road from monkeys to man it always starts with just one , unless we are to believe that the same favourable mutation takes place in 1000 creatures at the same time in the same place.According to our Darwinist friends a favourable mutation happens in creature x this mutation infers survival benefits and through creature x`s breeding this becomes established in the population then one of his offspring say creature y gets a favourable mutation which infers survival benefits and so on. So surely it starts with one. Thats if you believe such fairy tales.

I’m easy about the possibility of a single founding pair, or even special creation. But the idea of population genetics, as a standard explanation of speciation given common descent, shouldn’t be too hard to understand.

Take a small, isolated population of 10,000 of the precursor species – let’s call it Homo stupidus. That population has its own mix of gene alleles compared to the world population of H. stupidus, just as Finns or Melanesians have theirs.

This population then, over time, gets its own particular mutations, some of which get spread around. For Finns it would be fair hair and skin, for Melanesians something else. And so the whole population (always 10,000, always isolated) gradually changes from Homo stupidus to Homo sapiens, just as there was never a single pair of “Finns” or “Melanesians”, even though they differ a lot.

There are problems with that version of evolution, even allowing for my gross simplification – but it does show that thinking along the lines of “If there are lots of humans now, there must have been one or two humans at the beginning” is genetic nonsense.

Remember that both Richard Buggs and Ann Gauger are working on ways that a single pair might indeed be possible given the right circumstances. Most other circumstances demand larger evolving populations.

I’m reading Matushita Nei’s latest book. It seems that we must invoke “bottlenecks” since otherwise the percentage of heterozygosity would be very different for large and small populations, and this would debunk neutral theory.

Let’s all hear it for neutral theory.

(Or, at least ‘nearly-neutral’ theory; or whatever is the latest take on Kimura’s theory)